1. Field of the Invention
The invention relates to subsea assemblies used in offshore deep water operations and the production of hydrocarbons. In particular, the invention relates to systems, apparatuses and methods for rapid disconnection and reconnection of a marine drilling riser from and to a lower marine riser package. More particularly, the invention relates to modified release connectors, modified flex joints, a modified lower marine riser package, modified annular blow out preventers, annular-release flex-joint assemblies and resident ROV and sonar technology as well as novel methods to utilize these components.
2. Description of the Related Art
A subsea oil well may be accessed, for example, from a mobile offshore drilling unit (MODU), by a marine drilling riser (MDR) connected to a subsea blowout preventer (BOP) stack which is attached to a subsea wellhead. The MDR is a conduit that provides an interim extension of a subsea oil well to the surface drilling equipment and is used to circulate drilling fluid back to the drilling rig. In a conventional arrangement, the MDR may be connected via a riser adapter such as a flex joint to the uppermost annular BOP of the BOP stack. Two bolted flanges, one between the flex joint and the riser, and one between the flex joint and the uppermost annular BOP, are commonly used to effect this connection.
The MDR is connected to the BOP stack. The BOP stack comprises a lower marine riser package (LMRP) and a lower BOP stack. The MDR is connected to the BOP stack via the LMRP and the LMRP is situated above and connects to the lower BOP stack. The LMRP and the lower BOP stack are usually adjoined by a hydraulically actuated connector. Most often, the LMRP includes, for example, one or two annular BOPs while the lower stack comprises a series of ram BOPs of different types.
A prior art LMRP, includes a riser connector, a flex joint, annular blow out preventers, control pods, control lines and other components, all surrounded by a protective cage-like structure that provides structural integrity to the assembled system. The LMRP may also include, for example, the controls for both the annular BOPs of the LMRP and the ram BOPs of the lower stack, as well as (portions of) control lines such as kill, choke, hydraulic supply, boost, emergency bypass, an interface for a remotely operated vehicle (ROV) to operate the subsea system.
Currently accepted contingency for emergency well intervention/containment in deepwater is to disconnect the LMRP from the lower BOP, expose the connector mandrel on the top of the lower BOP, which would provide a connection point for a capping stack or similar containment system. In an emergency scenario with a prior art LMRP, should it not be possible to effect the disconnection of the LMRP from the lower BOP it may be necessary to effect a subsea disconnection of the MDR from the LMRP which would involve unbolting of the MDR from the riser adapter above the flex joint or other accessible adapter above the flex joint or unbolting the flex joint from the uppermost annular BOP. These scenarios would also require the bolting of a mandrel onto the exposed flange above the flex joint or to the uppermost annular BOP, and affixing another BOP, capping stack or containment system over the uppermost annular BOP or above the flex joint, similar to the intervention required on the BP Macondo subsea equipment. Affixing the capping stack above the flex joint is likely to be the only feasible option but introduces significant risk to the well control scenario as the flex joint is typically only rated to 5,000 psi working pressure, considerably less than the other components in the BOP system. Additionally, effecting these connections and disconnections, which would need to be done by underwater robotic vehicles, is complex, hazardous, costly and time-consuming.
In the case of an emergency such as the uncontrolled flow of oil from the well or failure of a BOP, the MDR may have to be disconnected from the LMRP, brought up to the drilling rig at the surface so as to provide access to the LMRP and its controls. The routine or emergency recovery of the MDR to the surface to facilitate access to the LMRP is also a very hazardous, costly, time-consuming and challenging procedure because of the MDR's significant size and weight. In deep water this operation could take several days and, therefore, significantly delay the installation of well control equipment in an emergency situation or cause significant drilling rig downtime during routing drilling operations.
Following the oil well blowout of the BP Macondo well in the Gulf of Mexico, government and industry interests have focused attention upon new and practical technology that facilitates the containment, control and suppression of a similar occurrence should a blowout occur sometime in the future. Most approaches, however, have been to enhance BOP functionality and to utilize an approach which integrates to existing subsea components and connection points instead of actively addressing the shortcomings of current components within the BOP unitization stack. Therefore, there is a need for an approach that would provide additional intervention capability than exists today allowing the use of a second blowout prevention system to re-enter the wellbore through the disabled equipment and attaching a plug, collection dome or capping stack with methods not currently available.
Embodiments of the present disclosure address the afore-mentioned shortcomings in the prior art. For example, the current invention provides for improved access to the LMRP during emergency or routine drilling operations, provides a means of effecting emergency well intervention or routine LMRP maintenance without the need to recover the MDR to the MODU, provides novel flex joints, connectors, annular BOPs, resident remote operated vehicles, sonar technology, mandrels with seal plates, higher annular bypass capabilities and alternative containment devices as well as flex joint-connector-annular assemblies that help reduce the height of the riser interface/LMRP/BOP stack and provide additional intervention options.